1. Field of the Invention
The present invention relates to a radiotherapy apparatus controller and a radiation irradiation method, and especially relates to a radiotherapy apparatus controller and a radiation irradiation method used when a patient is treated by irradiating an affected area with a radiation.
2. Description of Related Art
Radiotherapy for treating a patient by irradiating a therapeutic radiation to an affected area (a tumor) is commonly known. A radiation generated by the bremsstrahlung is exemplified as the therapeutic radiation. A method of an irradiation for a wider area than the affected area in consideration of a moving region where the affected area moves, a respiratory-gated radiotherapy (a gated irradiation), and a method of a dynamic tumor-tracking irradiation are known as the radiotherapy. The respiratory-gated radiotherapy is a method for irradiating the therapeutic radiation and stopping the irradiation based on a position of an affected area. The radiotherapy of the dynamic tumor-tracking irradiation is a method for changing an emitting direction or an irradiation field of the therapeutic radiation based on a position of an affected area. The respiratory-gated radiotherapy and the radiotherapy of the dynamic tumor-tracking irradiation are desirable since a dose of the therapeutic radiation irradiated to normal cells other than the affected area is smaller as compared to the radiotherapy of the irradiation for the wider area than the affected area.
In the respiratory-gated radiotherapy and the radiotherapy of the dynamic tumor-tracking irradiation described above, the position of the affected area is required to be consecutively measured. As a measurement method, an X-ray photography method and a MRI (Magnetic Resonance Imaging) method are exemplified. For a target (a lung tumor is exemplified) rapidly moving because of a physiologic movement such as a breath and a pulsating, it is required to shorten a period in which a target position in a body is observed (to increase frequency of the observation) in order to accurately know the target position. The more frequency of the X-ray photography increases, the more a radiation exposure of X-ray for the X-ray photography of a patient increases. Radiotherapy is desired in which a radiation exposure of a patient other than the therapeutic radiation can be reduced.
The law restricts a simultaneous irradiation of the X-ray used for the X-ray photography and the therapeutic radiation to a patient. The MRI needs to operate for a long period of time in order to accurately measure a position of an affected area. The MRI further needs to time-share the observing an affected area by the MRI and the emission of the therapeutic radiation in order to generate a strong magnetic field. For this reason, the more frequency of the observing a position of an affected area increases, the more time for which the therapeutic radiation is irradiated is reduced, and a treatment time will become longer. It is desired to reduce the treatment time of the radiotherapy and to reduce a strain of a patient.
It is desired to more accurately observe a position of an affected area and to reduce frequency of the observing the position of the affected area.
U.S. Pat. No. 6,144,875 discloses a technique for, as for a target moving by a breath, intermittently obtaining a position of the target inside a body by a first sensor and subsequently obtaining a position of the target outside the body by a second sensor, relating the two positions, and estimating the position of the target inside the body based on the position of the target outside the body and irradiating.
U.S. Pat. No. 6,307,914 discloses a technique for, as for a target moving by a breath, performing an X-ray photography at a predetermined frame rate by using two imagers, calculating a three-dimensional position of a marker inside a body base on the images, and irradiating a radiation to the three-dimensional position to treat it.